mz::type_list

A variadic 'type list' for performing operations on lists of types in metaprogramming contexts. Optimized to be much more compiler-friendly than std::tuple.

See Compilation speed humps: std::tuple for a write-up on the sorts of optimizations applied herein.

Requires C++17.

Synopsis

namespace mz
{
	template <typename... T>
	struct type_list
	{
		// get the number of types in the list:
		static constexpr size_t length = sizeof...(T);

		// index of the first appearance of the specified type:
		template <typename U>
		static constexpr size_t index_of = /* ... */;

		// determine if a specified type appears in the list:
		template <typename U>
		static constexpr bool contains = /* ... */;

		// get a specific type:
		template <size_t Index>
		using select = /* T...[Index] */;

		// convenience alias for select<0>:
		using first = select<0>;

		// convenience alias for select<0> when length == 1:
		using type = select<0>;

		// get a 'slice' (sublist):
		template <size_t Start, size_t Length = (length - Start)>
		using slice = type_list</* ... */>;

		// adding on to the beginning of the list:
		template <typename... U>
		using prepend = type_list<U..., T...>;

		// adding on to the end of the list:
		template <typename... U>
		using append = type_list<T..., U...>;

		// recursively flatten child sublists:
		using flatten = type_list</* ... */>;

		// remove all occurrences of the specified type:
		template <typename U>
		using remove = type_list</* ... */>;
	};

	// alias for a single-element list:
	template <typename T>
	using type_tag = type_list<T>;
}

Usage

The library is a single header so the easiest way to use it is to drop type_list.hpp somewhere in your project.

Alternatively you can add include to your include paths then #include <mz/type_list.hpp>

There is also support for use as a meson.build subproject.

Benchmarks

Single-threaded compilation of the example application on my Ryzen 3950X:

	Clang 12	GCC 10	MSVC 19.29
std::tuple	6.448s	3.185s	7.965s
mz::type_list	0.303s	0.407s	0.830s
speedup factor	21.2x faster	7.8x faster	9.6x faster

License

MIT. See LICENSE.

Contributing

There are three ways you can contribute:

1. Reporting bug or making feature requests here
2. Opening a pull request (⚠️ caveat - see below)
3. Becoming a sponsor ❤️

Pull requests

type_list.hpp is programmatically extracted from a much larger project so I won't accept pull requests made for this repository directly; if you wish to contribute a bugfix or a feature, please find the type_list implementation in this project and propose your changes there instead. I will then propagate them to this satellite library when they are merged.